Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already cover read-only, idempotent, non-destructive, and closed-world behavior, and the description adds useful disclosure about the full return contents. The note that it cannot look up by invoice number adds a concrete behavioral limitation beyond structured fields.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the return contents, then gives usage context and constraints in two short sentences. Every sentence carries actionable information with no repetition.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple one-parameter read-only tool, the description covers purpose, return shape, usage, ID provenance, and a key limitation. With annotations and schema already clear, nothing important for correct invocation is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the parameter's base meaning is already documented. The description still adds value by saying the invoice id should come from list_invoices and that invoice-number lookup is not supported.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: returns one invoice in full, and enumerates the returned contents (sender/recipient details, dates, totals, line items, discounts, payments). It is clearly distinguishable from list_invoices and update_invoice by naming both siblings and its scope.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly says to use it to review an invoice or to fetch complete current values needed by update_invoice, and specifies that the id comes from list_invoices. It also states a clear exclusion: it cannot look up by invoice number.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.